What does it take to launch a career in pop music? Being a Mouseketeer in the Mickey Mouse Club on TV, like Justin Timberlake or Britney Spears? A home video, like Justin Bieber? Art school? Twerking? There's no single answer.

Take the case of Betty Who, the rising star in the American dance-pop charts, who has just released her debut album to general acclaim. Her turning point came last year, when a fan choreographed a same-sex marriage proposal in a Home Depot store to Who's song, Somebody Loves You, and posted it on the internet.

With lightning speed, the 22-year-old singer has subsequently become the latest bright young thing to provide a lesson in how to construct a career with few of the conventional components.

In April 2013, the singer – born Jessica Anne Newham – self-released four songs as Betty Who. She didn't present herself as pop perfection: there were no stylists or viral marketing experts; no sex tape; no twerking. At 6ft 1in, she's hardly in the mould of Kylie Minogue, her fellow Australian, or Cyndi Lauper, with whom she is sometimes compared.

Fans are embracing the singer, who studied the cello and received a classical music education at Boston's Berklee College of Music, as a performer whose do-it-yourself, grassroots ethos has created an unusually potent pop construction – a singer whose talent and following has come naturally, rather than under the direction of a pop Svengali or management team that oversees every tweet or Instagram picture.

Who admits that she always knew she wanted to be a musician. But the cello couldn't compete with her love of big-sounding 1980s synth-pop. "I never fitted in within the classical world," Who told Billboard magazine. "I didn't have enough discipline with cello – I wanted to play because I loved it, not because I had to." So she switched to writing pop songs about teenage boys.

Initially, even her friends were surprised by her transformation. "That's me," she'd remind them. "Every time someone says 'Betty Who', it reminds me that I'm really doing it. I'm really pursuing what I always wanted to."

Success has come by appealing to a mass audience, while also maintaining credibility – an issue that dogs singers such as Lana Del Rey, whose image leaves fans having to guess which aspects are true or false. "I want people to feel safe listening to my music," Who told Time magazine recently. "I don't want them to feel like they don't get it." However, the success of the song that broke her in the US – the Cindy Lauper-Whitney Houston tribute-pastiche Somebody Loves You – owes a debt of gratitude to Spencer Reeser-Stout, a Salt Lake City man who popped the question to his boyfriend last September in front of a flashmob dance troupe. Reeser-Stout's "Home Depot Marriage Proposal" was posted on YouTube and went viral. It's now been watched 12m times. The couple married in front of millions of viewers at this year's Grammy awards, with Madonna officiating. Later, Who sang at their private ceremony.

"Millions of people have watched the video, but none of it compares to sitting and crying as they walked down the aisle with their mothers," Who later recalled. "I had to work really hard not to cry as I was singing."

Industry observers say that the circumstances of Who's success are not in themselves unconventional – building a fan base without a record deal is common – but the way it's done now is like launching an app. If the app is successful, then Facebook or Google – or a traditional record company – comes calling.

"This sounds very Disney, but I would rather have a song or image that reflects who I am," Who says. "I'm lucky to have the luxury to say that, because I had the first EP that I did really honestly and had it do very well. Otherwise, I could be saying that and I could be talking out my ass."

A singer or band that develops outside the industry and establishes a following independently also reduces the risk for record companies. In a sense, the traditional business of A&R scouts signing unknowns on a hunch has been taken over by big data metrics. The process also suggests authenticity, the elusive component that helps to translate flash-in-the-pan pop success into a "keepin' it real", sustained career.

"Even though she's obviously talented, she's an accidental pop star," says US manager-consultant Andy Gershon. Since it couldn't be conceived, it couldn't be marketed, hence it must be real: "Only in this day and age can someone proposing to your song make you a pop star. You couldn't market a viral video of someone proposing to your song to get you over the hump."

Gershon cautions that such realness is no guarantee of longevity. "But she has captured that one moment in time."